1. Field of the Invention
The present invention relates to a liquid crystal display device, and particularly, to a liquid crystal display device sealing structure and method of fabricating the same, wherein the seal structure includes a shield system that prevents impurities and moisture from infiltrating into the liquid crystal display device.
2. Description of the Background Art
A liquid crystal display (LCD) device is a permeation type flat panel display device, and is commonly incorporated into small power efficient devices, such mobile phones, personal digital assistants (PDA), and notebook computers. Presently, demand has increased for digital displays having improved image quality and mobility.
In general, the LCD devices can be categorized according to the method by which liquid crystal molecules are moved. One category of the LCD device is a thin film transistor (TFT) LCD that is commonly used for its rapid reaction speed and reduced amount of residual image. The TFT LCD is made by injecting liquid crystal material between a TFT substrate having a plurality of TFTs formed thereon and a color filter substrate having a color filter formed thereon, sealing the substrates together, and attaching necessary driving circuitry.
FIG. 1 is a cross sectional view of a liquid crystal display device according to the prior art. In FIG. 1, spacers 30 are disposed between a color filter substrate 10 and a TFT substrate 20 to maintain a cell gap, and a liquid crystal material 50 is injected therebetween. An outer circumference of the liquid crystal display device is sealed by a sealant 40 to prevent infiltration of impurities or moisture into the liquid crystal display device. In addition, a back light (not shown) is disposed under the TFT substrate 20 to provide light for the liquid crystal display device, and polarizing films (not shown) are attached to the color filter substrate 10 and the TFT substrate 20 to polarize the light provided by the back light (not shown).
FIG. 2 is an enlarged cross sectional view of a portion “A” of FIG. 1 representing a sealing structure of the liquid crystal display device according to the prior art. In FIG. 2, a black matrix 12 is formed on the color filter substrate 10 to prevent light from leaking through regions adjacent to a color filter layer 14, and a gate insulating layer 22 and a passivation layer 24 are formed on the TFT substrate 20. In addition, a common electrode (not shown) is formed on the color filter substrate 10 and a pixel electrode (not shown) is formed on the TFT substrate 20, and alignment layers (not shown) are formed on each of the color filter and TFT substrates.
In general, the sealing unit 40 is changed according to an overall size of the liquid crystal display device. Accordingly, the sealing unit 40 should be increased as the size of the liquid crystal display device increases to maintain a predetermined adhesive force between the color filter and TFT substrates 10 and 20. Thus, if the color filter and TFT substrates 10 and 20 are not sufficiently attached by the sealant, impurities or moisture may infiltrate into the liquid crystal material 50, and stains may be generated on a surface of the liquid crystal display device. In addition, the infiltration of the impurities or moisture into the liquid crystal material 50 may be caused by incomplete hardening of the sealing unit material.
FIG. 3 is a cross sectional view of a sealing structure and spacer pattern of a liquid crystal display device according to the prior art. In FIG. 3, a spacer pattern 32 is used for improving an aperture ratio of the liquid crystal display device by preventing uneven distribution of the ball spacers 30 (in FIG. 1). However, as discussed above, stains may also be generated due to incomplete sealing of the spacer pattern 32.
FIG. 4 is a cross sectional view of a liquid crystal cell structure of a liquid crystal display device according to the prior art. In FIG. 4, a liquid crystal cell includes a TFT substrate and a color filter substrate. The TFT substrate has a transparent glass substrate 21, a gate electrode 23a and a gate pad 23b formed on the transparent glass substrate 21, a gate insulating layer 22 formed on an entire surface of the glass substrate 21 to cover the gate electrode 23a and the gate pad 23b, a semiconductor layer 25 formed on the gate insulating layer 22, source and drain electrodes 27 formed on the semiconductor layer 25, a pixel electrode 29 made of a transparent conductive material, such as indium tin oxide (ITO), connected to one of the source and drain electrodes 27 and formed on the gate insulating layer 22 of displaying area on the liquid crystal panel, and a passivation layer 24 formed on the entire surface of the TFT substrate. The color filter substrate has a transparent glass substrate 11, a black matrix 12 formed on a region of the glass substrate 11 corresponding to the TFT formation region and the gate pad 23b formation region of the TFT substrate to block the light permeation to a non-displaying region, and a color filter layer 14 formed on the displaying region of the liquid crystal display device. In addition, the liquid crystal cell includes a common electrode (not shown) formed on the color filter substrate corresponding to the pixel electrode 29, and an alignment film (not shown) formed on the color filter and TFT substrates for aligning liquid crystal molecules in the liquid crystal material 50.
The liquid crystal display device includes an N×M matrix array of the liquid crystal cells formed on the entire substrate to form a liquid crystal display panel. The spacers 30 (in FIG. 1) are located between the color filter substrate and the TFT substrate fabricated as above, and the sealant unit 40 is applied on an outer circumferential portion of the TFT substrate. Then, the color filter and TFT substrates are attached using high pressure and high temperature. In addition, the liquid crystal material is injected between the color filter and TFT substrates, thereby completing fabrication of the liquid crystal display device.
The sealant material of the sealing unit 40 (in FIG. 3) is disposed along an outer circumference region of the liquid crystal display device, such that thin film transistors of the TFT substrate are located within the circumference region and the gate insulating layer 22, and the passivation layer 24 remains within the circumference region shown in FIG. 4. Thus, the sealing unit 40 is disposed upon the gate insulating layer 22 and the passivation layer 24.
In FIG. 4, the liquid crystal cell comprises an ITO-on-Passivation (IOP) structure. In the IOP structure, although the pixel electrode 29 is formed on the passivation layer 24, a first gap between a gate line 23b for supplying a scan signal to the gate electrode 23a and the pixel electrode 29 and a second gap between a data line (not shown) for supplying an image signal to the pixel electrode 29 through the source/drain electrode 27 and the pixel electrode 29 should be maintained. Accordingly, if the gate line 23b or the data line (not shown) overlaps a part of the pixel electrode 29 with the passivation layer 24 therebetween, a parasitic capacitance is created and a vertical crosstalk is generated. The crosstalk causes flicker of a displayed image, and lowers image quality of the liquid crystal display device.